The present invention relates to alginate fibres and a process for their preparation and their use. In particular the present invention relates to an implantation composition comprising alginate fibres.
A number of methods for producing conventional alginate fibres are described in the art. The extrusion of alginate solutions into an aqueous solution containing calcium ions to form calcium alginate filaments is known, for example, from British Patent Specifications Nos. 567641, 568177, 571657 and 624987. The replacement of a proportion of the calcium ions in calcium alginate by sodium ions to produce a more soluble fibre is known from British Patent Specification No. 653341.
Alginate is a heterogeneous group of linear binary copolymers of 1-4 linked .beta.-D-mannuronic acid (M) and its C-5 epimer O-L-guluronic acid (G). The monomers are arranged in a blockwise pattern along the polymeric chain where homopolymeric regions (M blocks and G blocks) are interspaced with sequences containing both monomers (MG blocks). The proportion and sequential arrangement of the uronic acids in alginate depend upon the species of algae and the kind of algal tissue from which the material is prepared.
Commercial alginates are produced mainly from Laminaria hyperborea, Macrocystis pyrifera, Laminaria digitata, Ascophyllum nodosum, Laminaria japonica, Eclonia maxima, Lesonia negrescens and Saragassum sp.
Alginate fibres have been known for some time as being useful in the preparation of wound dressings. For example, EP 433354 describes a wound dressing comprising a backing layer and a wound contact pad, the latter comprising a mixed salt alginate. EP 476756 describes a non-woven alginate fabric useful for the preparation of wound and burn dressings, the fabric being characterised in terms of its absorptive properties whereby the absorbency of the fabric is greater than 25.0 grams of deionised water or 19.0 grams of saline water per gram of fabric.
Alginates have also been used in transplantation and implantation compositions, however this use of alginates has been somewhat problematic due to immunogenic responses which have been observed. For example, Lim and Sun ((1980) Science 210, 908) microencapsulated islets using alginate gel, poly-L-lysine and polyethylenimine. The encapsulated islets were injected intraperitoneally into diabetic rats. The animals' blood glucose levels dropped to normal for two to three weeks, suggesting that the encapsulation process had protected the islets from invasion by the recipients' immune system. However, these studies showed that the microcapsules were eventually rejected as a result of fibrosis, or fibroblast formulation around the microcapsule, which eventually restricts the flow of nutrients to the cells contained in the microcapsule and the outflow of material from the microcapsule created by the islet cells disposed therein.
WO91/07951 describes a transplantation or implantation composition which provokes a reduced immune response and which employs an alginate comprising greater than 50% L-guluronic acid. The compositions described by WO91/07951 would not however be bioerodible when incorporated within the body cavity.